This invention relates to improvements in carving blanks and mandrels for mounting same in computer controlled carving machines particularly those used in prosthetic and orthotic applications.
Polyurethane foam blocks, otherwise referred to herein as carving blanks, of various shapes and sizes are typically used to produce three dimensional positive molds for use in the prosthetics and orthotics industry. To produce these molds, the foam blanks are typically mounted on a mandrel which is then fitted into a numerically (computer) controlled carving machine. The mandrel is rotated at a high speed while a drilling tool controlled by the machine's computer is moved in predetermined manner relative to the mandrel to carve out the predetermined shape.
Some of the problems associated with the prior art techniques were that the carving blanks were difficult to mount and dismount from the mandrel. It was also possible to mount the blank in more than one angular orientation relative to the mandrel, this being considered undesirable by those skilled in the art. The major reason for this is that unless the carving blanks were cylindrically symmetric it was difficult to ensure that free form shapes whose sizes were close to that of the block would actually fit inside the block and not have missed portions. At higher speeds the carving blanks tended to rotate or slide during the carving process. Two commonly used prior art blanks are known respectively as Regnier blanks and IPOS blanks. The first blank mentioned above required a large volume (footprint) of the blank to be used for the mounting hardware thus resulting in excessive wastage of material and there were two possible ways of mounting the blanks on the mandrel which, as noted above, is considered undesirable in this particular field of art. The second blank mentioned above tended to be somewhat difficult to manufacture in that the initial key used to mount the blank on the mandrel could not be easily freed from the mold after the molding process. A certain amount of manual manipulation was required to produce the final product. In use, the blank tended to be difficult to mount as a locking key and several screws had to be used to secure the blank to the mandrel. This design also tended to use a large volume of carving blank for the mounting hardware thus resulting in a wastage of time and materials.